So far, we've marked the end plates and side pieces for the screw holes (including holes for the middle cross members). If I count the number of holes I've marked, I should have a total of 40 holes that need to be drilled.
Your pieces of wood should now be marked up as shown below.
Our next step(s) will be to drill holes for #6 Robertson flathead wood screws 1 1/2" long. Drilling the holes will be either a 1-step or a 2-step operation, depending on the kind of drill(s) you have. I use an all-in-one drill with "countersink" (formally known as a "screw digger set" that I got at my local Home Hardware, catalogue #1227W540).
You may be tempted to use gyproc screws. Please don't. The countersink on a gyproc screw is entirely different from that of a regular wood screw. The gyproc screw is designed to hold gyproc in place so it has a flare, rather than a 60 degree angle, on the countersink. If you use gyproc screws in pine (or spruce), it will crack the wood with that final torquing.
If you don't have a combination drill/countersink, first drill pilot holes with a 1/8" drill bit followed by a 1/4" drill bit. Be careful when countersinking! We only want to pierce the wood a bit. When we install the screws, the screw head will more than disappear below the surface of our wood.
Here's a closeup of some of our drilled holes. Make sure your holes are 90 degrees in all direction to the surface of the wood.
And here's what the final product looks like. We've included the end plate of our second module in the photo as we'll need that second end plate when we install some more T-nuts for alignment pins/ bolts.
Next we install some more T-nuts for carry plates (pieces of plywood that will make a nice boxed set of our two modules).
PS - Here's a tip on how to easily clean your track - something called "rust erasers".